Multi-tubular reactors are used in many chemical processes, for example, catalytic chemical processes. Generally, multi-tubular reactors are arranged as a bundle having multiple parallel reaction tubes. In catalytic processes, the reaction tubes can contain a fixed catalyst bed. The reaction tubes can be vertically-oriented, allowing the chemical reactants to flow downwards, and through the catalyst bed. The multiple reaction tubes are generally connected by a feed header, which apportions the chemical reactants to the reaction tubes.
In certain processes, it is desirable to heat a multi-tubular reactor, for example, in order to heat an endothermic reaction and alter the equilibrium point of the chemical reaction. In such situations, a multi-tubular reactor can be placed within a furnace to provide heat to the reaction tubes. A furnace can provide both radiant heat, e.g., from a burner, and convective heat, e.g., from a flue gas. However, placing a multi-tubular reactor within a furnace poses certain design challenges. For example, although it can be advantageous to heat the reaction tubes with both radiant and convective heat transfer, radiant heat transfer can cause hot spots to form on the walls of the reaction tubes, leading to undesirable side reactions, e.g., cracking and coking of reactant or product molecules. Further, to optimize the temperature profile of the chemical reactant, it can be advantageous if the flow of the flue gas is co-current with the flow of the reactants, and ideally, has no horizontal velocity component if the reaction tubes are vertical. Co-current flow can also maintain an appropriate temperature distribution along the walls of the reaction tubes, for example, to avoid high temperatures at the bottoms of the reaction tubes where chemical products, which may be more prone to coking, are present.
Additionally, the multi-tubular reactor should be designed to permit periodic access to the catalyst beds for change-outs of spent catalyst, but for safety reasons, must also be completely sealed off from the flue gas. For example, catalyst beds can be accessed through the feed header, but if the feed header is disposed within the flow of the flue gas, it must be made of a heat resistant material and heat from the flue gas can cause fouling or coking within the feed header.
Certain multi-tubular reactors are known in the art. For example, U.S. Pat. No. 8,134,040 discloses a reaction panel including a feed header, a product header, and parallel reaction tubes from the feed header to the product header, each containing a catalyst. The catalyst can be accessed via detachable portions of the feed header and/or product header. FR2676222 discloses a fixed bed multi-tubular reactor for producing olefins that is heated radiantly, and operated in two stages: a reaction and a catalyst regeneration stage. International Publication No. WO2002/026370 discloses a process for catalytically reacting a fluid reactant stream in a multi-tubular reactor. The reaction tubes of the multi-tubular reactor have one or more rod-shaped inserts to promote heating or cooling of the reactant or product stream and curb side reactions in the product stream. U.S. Patent Publication No. 2011/0160314 discloses a reactor including multiple reaction tubes, which pass through a coolant chamber enclosed by top and bottom horizontal plates. The reaction products and the coolant preferably flow co-currently upwards through the tubes and chamber.
However, there remains a need for improved techniques for efficiently heating multi-tubular reactors. The present disclosure addresses these and other needs.